If statements in Linux terminal Post: 302861175

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Homework and Emergencies Homework & Coursework Questions If statements in Linux terminal Post 302861175 by sea on Tuesday 8th of October 2013 09:52:43 AM

10-08-2013

Registered User

First time i see constantly used the ( for if statements, i'm used to [..

Regard 'if statements'...
[[ condition ]] && echo succeeded || echo failed

Example:
[[ -z $XDG_DESKTOP_DIR ]] && echo "Your desktop is: $XDG_DESKTOP_DIR" || echo "$HOME/.config/user-dirs.dirs not loaded yet."

Which is the same as: (note the '\', that tells the line isnt dont yet, there must be no trailing spaces!)

Code:

[[ -z $XDG_DESKTOP_DIR ]] && \
    echo "Your desktop is: $XDG_DESKTOP_DIR" || \
    echo "$HOME/.config/user-dirs.dirs not loaded yet."

Which i prefer for 'short code' like setting a variable.

The && is appending the following command if previous command returns 0/true.
The || indicates what is done if the previous condition/command failed.

Examples:

Code:

[[ ! 0 -eq $UID ]] && echo "You're not root, and we abort" && exit
[[ 0 -eq $UID ]] || echo "You're not root, but we continue anyway"
[[ 0 -eq $UID ]] && echo "Must not be root!" && exit || echo "You may pass $USER"

hth

Last edited by sea; 10-08-2013 at 11:03 AM.. Reason: uh.. wasnt asked.. but since we're on it..

sea

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LEARN ABOUT OPENSOLARIS

noecho

echo(3XCURSES)						  X/Open Curses Library Functions					    echo(3XCURSES)

NAME

       echo, noecho - enable/disable terminal echo

SYNOPSIS

       cc [ flag... ] file... -I /usr/xpg4/include  -L	/usr/xpg4/lib 
	-R  /usr/xpg4/lib  -lcurses  [ library... ]

       c89 [ flag... ] file... -lcurses [ library... ]

       #include <curses.h>

       int echo(void);

       int noecho(void);

DESCRIPTION

       The  echo()  function enables Echo mode for the current screen. The noecho() function disables Echo mode for the current screen. Initially,
       curses software echo mode is enabled and hardware echo mode of the tty driver is disabled. The echo() and noecho() functions control  soft-
       ware echo only. Hardware echo must remain disabled for the duration of the application, else the behavior is undefined.

RETURN VALUES

       Upon successful completion, these functions return OK. Otherwise, they return ERR.

ERRORS

       No errors are defined.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Unsafe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       getch(3XCURSES), getstr(3XCURSES), initscr(3XCURSES), libcurses(3XCURSES), scanw(3XCURSES), attributes(5), standards(5)

SunOS 5.11							    5 Jun 2002							    echo(3XCURSES)